Well other than the same reason that he didn't watch Vi feed. Which is the fact he is the one that did this to Avina. From how he acted after drinking from Avina, it can be a very intimate thing, causes both intimate thoughts and feeling while feeding. And if she feeds from a man it could cause a bit of jealousy. 

Plus I have a bit of a feeling that with the blood thirst being doubled from being hybrids, he might have to step in to keep her from drinking the person dry. That can make her get sick, and it would be a waste of blood.